The present invention relates in general to devices for the individual feeding of sheets from a stack, and in particular to a new and useful pneumatic sheet feeder which includes a single blower for establishing an air cushion between sheets to be fed, and for establishing a suction in a suction cylinder for pulling off individual sheets from the stack.
Sheet feeders of this kind may be employed for removing individual sheets consecutively from a stack and delivering them in predetermined intervals to packaging machines, printing presses, labeling and marking machines, etec. By means of blast nozzles provided in guide rails, air is blown against the lowermost sheets of a stack, whereby at least thin air cushions are formed between the individual sheets, thus facilitating the removal of a single sheet at a time from the bottom of the stack. By means of a suction cylinder, the leading edge portion of every lowermost sheet is engaged by suction, and advanced below the limiting edge of a stop plate which is fixed, yet adjustable to different sheet thicknesses, to conveying means downstream of the stack, for further transportation.
In prior art feeders of this kind, separate devices, namely a blower and an exhauster, are provided for supplying the blast nozzles with compressed air, and producing a vacuum in the vacuum chamber of the suction cylinder, with the blower being in permanent connection with the blast nozzles, while the exhauster is connected to the vacuum chamber only periodically, in intervals timed by means of a solenoid valve in accordance with the operating cycle of the machine.
These prior art apparatuses require not only two different devices for blowing and exhausting, but also bypass lines which considerably increase manufacturing costs.